Manometer with direct passage

ABSTRACT

A direct passage manometer includes a body into which at least two rectilinear channels open into a recessed curved surface at a central portion thereof. A diaphragm seals the curved surface at the center of the body and is fixed in place by a load cell. The load cell has a movement amplifying device and indicator mounted thereon. The movement amplifying device rests on the diaphragm, connects to the indicator and is fixed in place by the load cell. The opening holes of the two channels are elliptical in profile and machined so as to avoid any retention zones.

This application is the US national phase of international applicationPCT/FR00/01773 filed Jun. 23, 2000 which designated the U.S.

FIELD OF THE INVENTION

The present invention relates to a device for pressure measurement on aline of various installations. It relates more particularly to amanometer whose design makes it possible, on the one hand, to avoid anydead space in the driving element, and on the other hand to offer veryeasy cleaning without the need to disconnect the measuring instrumentfrom the process line or even dismantle it.

BACKGROUND OF THE INVENTION

Manometers of conventional design, whether of the Bourdon tube, capsule,or bellows type, etc., have driving elements containing a relativelylarge dead space, in which the fluid to be measured remains trapped.

In manometers of this type, it is in fact very difficult, if notimpossible, to clean the said driving element, which is at a real deadend that is impossible to reach. Finally, the fluid whose pressure isbeing measured remains permanently trapped inside the driving element.For certain industries and applications, this phenomenon may betroublesome, because undesirable germs and bacteria can grow andmultiply inside this dead end. Moreover, it is obvious that by virtue ofits very shape, a Bourdon tube or bellows—whether it is drawn withoutwelding, or rolled and welded then drawn—cannot have a perfect internalsurface condition whatever treatments are applied to it.

Assuming that the internal surface condition is correct, the weldsproduced—at the end of the tube and for fixing the tube to theconnector—give rise to the presence of impurities inside the tube.

Treatments such as electropolishing, treatment in the “extrudom” orother treatments, may claim to improve the internal surface condition ofa really small part of the Bourdon tube, but in no case can they make itsufficiently clean and free from all impurities.

Conventional driving elements, of whatever form (Bourdon tube, bellows,capsule, etc.), prove to be real pockets for particles, which areimpossible to clean efficiently, and whose internal surface condition incontact with the medium to be measured is incompatible with industriesrequiring high degrees of cleanliness and purity.

Furthermore, during changes in manufacture, the user may wish to cleanthe lines and the measuring instruments that are installed on thelatter. In the case of manometers, such cleaning is impossible, unlessthe manometer is separated from the installation by means of anintermediate component, called a separator. This separator makes itpossible to isolate the measuring instrument from the line, and servesas a “buffer”. The separator is equipped with a diaphragm that is incontact with the fluid to be measured, whilst a filling liquid(generally an oil) provides transmission of the pressure existing in theinstallation between this diaphragm and the driving element of themanometer.

The use of a separator may give rise to problems and is not alwaysideal. The performance of a separator largely depends on the mechanicalcharacteristics of the diaphragm itself (its response curve), on thequality of the filling liquid, its thermal stability, its viscosity, thefilling conditions, etc. In addition, hermeticity between this diaphragmand the line of the installation is provided by a seal, which alsooffers retention zones where germs, bacteria and microbial flora candevelop.

Furthermore, the use of a filling liquid in the separator means there isa risk of contaminating the entire installation equipped in this way, ifdiaphragm rupture occurs.

In addition, a separator is an added item, independent of the manometer,which adds an extra cost to the final product.

Even so, manometers, whether or not they are mounted on a separator, arereliable instruments for measuring pressure, whose performance meets therequirements of the majority of industrial applications.

There are fields of application or industries where the drawbacksmentioned above become preponderant. This applies in particular to thefood and agricultural industries, fine chemicals, the pharmaceuticalindustry, the semiconductor manufacturing industry, industries producingor using pure, rare and toxic gases, industries where pressure measuringinstruments are used in painting processes, etc.

In all these industries or applications, the use of pressure measuringinstruments demands very stringent precautions, especially with regardto the presence of impurities, germs, dust etc. The measuringinstruments used in these types of processes must be able to be cleanedvery easily.

In food and agricultural industries, for example, the processors need tomeasure the pressure of foodstuff liquid or pastes intended for human oranimal consumption. Consequently, equipment for carrying out thesemeasurements must never under any circumstances allow the growth anddevelopment of germs or bacteria that might alter or contaminate thefoodstuffs whose pressure is being measured. Therefore the measuringinstruments must be designed in such a way that the retention zones arealmost non-existent, and in such a way that they are easy to clean (i.e.they must be designed in such a way that they can easily be cleaned bypassing cleaning products, hot water, or other decontaminating productsthrough the lines of the installation).

Similar problems arise in the pharmaceutical industry, fine chemicalsindustry, etc.

In the field of gas distribution in the semiconductor industry,manometers are mainly used for measuring the pressure of two groups ofgases:

Gases that are called “pure gases”, which have extremely exactingrequirements in terms of purity: ultrapure nitrogen; argon; helium; etc.These are generally gases for which the degrees of purity may reach orexceed 99.99999%.

Gases called “doping gases”—generally highly toxic gases (arsine,boron—gallium, etc.)—for doping the silicon wafers on which electroniccomponents are produced, such as memories (RAM, DRAM), microprocessors,etc.

In this industry it is necessary to employ measuring instruments thathave been made following very rigorous procedures in terms ofcleanliness, so that there is no risk of contaminating the gases thatare used.

Furthermore, all retention zones are forbidden, because, in this casetoo, they promote the development of undesirable germs or bacteria.

Moreover, for example in pressure measurement on lines for paintingprocesses, depending on the operations being carried out, the pressuremeasuring instruments have to measure the pressure of paints ofdifferent colours. Between two manufacturing operations, the manometersmust be easy to clean and must not have any retention zones where paintfrom the previous manufacturing operation might contaminate the nextmanufacturing operation.

The examples given above are not limiting. There are many othermanufacturing processes where the measuring instruments installed on theproduction lines must be as easy to clean as possible, with a designthat does not permit any retention zones promoting the development ofgerms, bacteria and other substances that could contaminate theproduction process or the constituents that are involved in the saidproduction process, such as, in particular, liquids, gases, etc.

It is clear from the foregoing that these instruments must, as far aspossible, be able to be cleaned or rinsed. In this context, it can beseen that conventional manometers do not offer this facility by anymeans, and that their use poses enormous problems, unless they arecombined with separators.

To overcome these drawbacks, the main manufacturers of pressuremeasuring instruments have in recent years developed devices called“full-bore pressure transmitters” which avoid these contaminationproblems. In fact, various technologies derived from recently developedtechnologies in electronics have made it possible to devise pressuremeasuring instruments in which the driving element (the element thatmakes it possible to transform a physical quantity—pressure—into anelectrical signal) is quite simply a tube, and the “fluid” whosepressure is to be measured circulates inside this tube. There are, forexample, pressure transmitters that are completely free from retentionzones and that offer maximum ease of cleaning. This equipment consistsof a tube, on which a flat surface is machined, the dimensions andmachining tolerances of which are known precisely. Film-screen straingauges, arranged as a Wheatstone bridge (a network of resistances), arecarefully positioned and glued on this flat surface. When this networkof resistances is supplied with an external voltage, the Wheatstonebridge supplies an electrical signal whose value varies as a function ofthe deformation of the strain gauges when a pressure is exerted on theinside wall of the tube (at the level of the flat surface).

The output signal of the Wheatstone bridge therefore depends on thevalue of the resistances glued to this flat surface. The flat surfacetends to be distorted under the action of the pressure. As it deforms,the flat surface also causes the strain gauges to undergo deformations,which are finally translated into a change in the value of each of theresistances or strain gauges. An immediate consequence is a changeand/or deviation of the output signal at the terminals of the Wheatstonebridge under the action of the pressure. On the whole, the output signalis proportional to the deformation of the flat surface and hence to thepressure exerted by the fluid circulating in the tube on the zone ofdeformation of the said flat surface. The output signal of theWheatstone bridge is then processed by an electronic system thatgenerally supplies a current between 4 and 20 mA, correspondingrespectively to zero pressure and to the maximum pressure for which themeasuring instrument has been calibrated.

Transmitters of this type meet in full the requirements of cleanliness,purity and cleanability. But their use is subject to other constraints,the most important of which, for the user, is the need to provide anelectrical supply to the Wheatstone bridge and hence to this type ofpressure transmitter. The end user therefore has to make provisions forthe laying of power cables on the installation and process for thisequipment. In the semiconductor industry, for example, it is notuncommon to install several hundred pressure measuring instruments formonitoring the distribution of gases in the manufacturing process. Plantof this type can be heavy and expensive. Furthermore, only transmittersof this type must be combined with a unit for visualizing themeasurement transmitted by the instrument: a display will permitvisualization of the line pressure in real time.

Finally, a transmitter is usually more expensive than a manometer.

SUMMARY OF THE INVENTION

The present invention therefore aims to overcome these drawbacks, byproposing a device that is independent of any driving element and isautonomous in terms of energy source, and can largely eliminate problemsconnected with the purity, cleanliness and cleanability of the drivingelement.

For this purpose, the direct-passage manometer of the invention ischaracterized in that it has a body that is provided at its center witha hollowed curved surface, into which at least two transverse holesopen, to allow the entry and exit of the fluid whose pressure is to bemeasured, this curved surface being sealed off by a diaphragm that isheld in position on its seating by a load cell which interacts with thebody via fixing means and orifices, the load cell being provided inaddition with second fixing means for mounting a movement amplifyingdevice resting on the diaphragm and connected to an indicator.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention willbecome clear from the description given below, referring to the appendeddrawings illustrating an example of application thereof, which is in noway limiting. In the diagrams:

FIG. 1 is a plan view of a manometer according to the invention;

FIG. 2 is a sectional view and side view of FIG. 1;

FIG. 3 is a plan view of the body of the manometer;

FIG. 4 is a sectional view and side view of a diaphragm used in themanometer of the invention;

FIG. 5 shows a variant of implementation of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

According to a preferred embodiment, reference may be made to FIGS. 1and 2, in which the manometer body is represented by 1, the diaphragm by2 and the load cell by 3, these three components being assembledtogether so as to form the manometer.

The body 1 is produced in a succession of machining operations so as toproduce an approximately cylindrical component forming a base. The saidcomponent 1 is preferably machined in a metal draw frame especially ofthe stainless steel type, and has, roughly at its center, a recessedcurved surface 4, for which the radius of curvature, the machining, thesurface treatment and the surface condition make it possible toeliminate any retention zones, so that this manometer can be cleanedperfectly while in line.

At least two transverse holes 5, 6 open into the said curved surface 4and their purpose is to permit the entry and exit of the fluid whosepressure is to be measured.

According to a first embodiment, these holes 5, 6 are positioned on thesame generating line, especially on a diameter of body 1 (cf. FIG. 3).

According to a second embodiment, these holes 5, 6 are positioned on twointersecting generating lines (cf. FIG. 5).

Whatever the manner of implementation, the zones of intersection betweenthe holes 5, 6 and the recessed curved surface 4 form an ellipticalprofile in which the connecting zones are also machined and treated insuch a way as to avoid any retention zones.

According to another characteristic of the invention, the periphery ofthe recessed curved surface 4 is provided with a ring 7 which delimits acountersink that serves as a contact surface for the diaphragm 2.

The said diaphragm 2 completely covers the recessed curved surface 4 andreceives the pressure forces resulting from passage of the fluid acrossthe cavity via the two holes 5, 6 (cf. FIG. 4).

Diaphragm 2 is in the form of a metal disk having a plurality ofconcentric undulations 8, between which are delimited elastic strainzones.

In addition, the central part 9 of the said diaphragm is flat anddelimits a zone of contact with a movement amplifying device, which isitself connected to a pinion which causes movement of a pointer on itsshaft.

Furthermore, the peripheral part 10 of diaphragm 2 is flat and ispositioned approximately in a median plane relative to the large numberof concentric undulations distributed between the central part 9 and theperipheral part 10 of diaphragm 2. The role of this peripheral part 10will be explained later.

Moreover, the said diaphragm 2 is obtained in particular by a drawingoperation in metal strip which will then undergo a number of heattreatment operations as well as a number of surface treatmentoperations.

The choice of materials used and their treatments was rigourouslystudied and selected so as to permit optimum functioning, and inparticular so as to offer excellent metrological performance (linearity,hysteresis, repeatability), and accordingly accuracy class 1 isachieved.

The body 1 of the manometer also has a number of fixing means 11,preferably equally spaced around ring 7.

These fixing means 11 are produced by drilling and tapping in body 1 ofthe manometer, so as to permit solid mounting of load cell 3.

Load cell 3 is made of a material similar to that of body 1, in a numberof conventional machining operations as well as various operations ofsurface treatment.

Cylindrical overall, in the form of a hoop, this component is intended,on the one hand, for holding the diaphragm above the curved-surfacecavity 4, and on the other hand for providing the mounting for themovement amplifying device as well as the graduated dial.

Thus, for performing these various functions, the hoop forming the loadcell 3 has a number of holes 12 with angular positioning so that theymatch up with the fixing means 11 provided in body 1 of the manometer.

These holes 12 allow the passage of screws, studs or the like, whichinteract with the fixing means 11 and make it possible, by tighteningthe screws, for load cell 3 to be held on body 1.

According to another characteristic of the invention, since the face ofthe hoop has to be in contact with the peripheral part 10 of diaphragm2, it has a shoulder or annular projection which delimits a contactsurface 13 which permits, during mounting of load cell 3 on body 1,clamping of the peripheral part 10 at the level of the countersink 7made in body 1.

Assembly of the manometer, at the level of the body 1 of diaphragm 2 ofload cell 3, is effected without welding, and therefore without any riskof internal contamination. Installation of the manometer is of class100, and of class 10 (under hoods with laminar flow) for certainoperations, to avoid any risk of contamination.

Load cell 3 also has second fixing means 14 for mounting the measurementamplifying device, one end of which rests on the central part 9 ofdiaphragm 2, with the other end formed by a shaft for mounting theindicator, in particular in the form of a pointer.

In addition, the front part of hoop 3 has a series of shoulders 15 forpassage of the dial, which rests on the fixing means 14, as well as forholding a cover which protects the dial and the pointer.

According to yet another characteristic of the invention, as shown inFIG. 1, holes 5 and 6 are connected to branch pieces that projectlaterally relative to body 1 of the manometer. These branch pieces 16,17 receive various types of standardized, male or female connectingmeans, so as to permit installation of the manometer on the processline.

The invention as described above offers many advantages since themanometer constructed in this way has direct passage, with theparticular feature of offering zero dead space, and moreover the cavityfor measuring the pressure of the fluid is completely swept by the saidfluid, thus preventing any retention zone that might adversely affectcriteria of cleanliness.

Moreover, the construction, the form of the internal components, themachining operations, treatments and the surface condition of thevarious components forming the manometer make it possible to eliminateany retention zones, so that this manometer can be cleaned perfectlywhile in line. Owing to its design—with crimped rather than weldeddiaphragm—each component of this manometer can be treated so as toachieve an extremely high level of purity and cleanliness.

Of course, the present invention is not limited to the examples ofapplication described and illustrated above, but encompasses allvariants thereof.

What is claimed is:
 1. A direct-passage manometer comprising: a bodyhaving a recessed curved surface at a central portion into which atleast two channels open along intersecting lines for permitting directpassage entry and exit of fluid whose pressure is to be measured; adiaphragm that seals said curved surface and that seals against aseating member of said body; a load cell which holds said diaphragmagainst said sealing member by first fixing means; a movement amplifyingdevice that rests on said diaphragm and that is connected to anindicator, said movement amplifying device being mounted on said loadcell and being secured thereto by second fixing means; wherein said atleast two channels are rectilinear and radial relative to said body andhave opening holes into said recessed curved surface that form anelliptical profile, said opening holes being machined and treated so asto avoid any retention zones.
 2. A manometer according to claim 1,wherein the channels are positioned along a diameter of said body.
 3. Amanometer according to claim 1, wherein the channels are positionedalong two intersecting radii of said body.
 4. A manometer according toclaim 1, wherein a periphery of the recessed curved surface is providedwith a ring which delimits a countersink serving as a contact surface ofthe diaphragm.
 5. A manometer according to claim 4 wherein a face of theload cell, which is in contact with a peripheral part of the diaphragm,has a shoulder or annular projection that delimits a contact surfacewhich permits, during mounting of the load cell on the body, crimping ofthe peripheral part of the diaphragm at the level of the countersinkmade on the body.
 6. A manometer according to claim 1, wherein thediaphragm is in the form of a metal disk that has a number of concentricundulations between which are delimited zones of elastic strains.
 7. Amanometer according to claim 1, wherein a central part of the diaphragmis flat and delimits a zone of contact with the movement amplifyingdevice.
 8. A manometer according to claim 1, wherein a peripheral partof the diaphragm is flat and is positioned approximately in a medianplane relative to the large number of concentric undulations distributedbetween a central part and a peripheral part of the diaphragm.